Field of the Invention
This invention relates to improved fiber reinforced tubing and to the method and apparatus for fabricating it on a continuous basis. The apparatus contributes to the production speed and the quality and consistency of product inherent in the method.
Shobert U.S. Pat. No. 3,007,497, issued Nov. 7, 1961, describes the formation of a braided tubular structure formed by helically winding first and second sets of fiber reinforcing strands in mutually opposite directions around a mandrel while simultaneously moving the spools containing the fiber strands alternately in and out with respect to each other and to a third set of strands fed longitudinally into the braid. The third set of strands, which have since come to be known in the industry as "stud fill", help lock the helically wound strands into a reinforcement structure of greater integrity than had been possible prior to that time. However, the dry fiber was braided in a fixed position on the mandrel, which was fed through the braider at a rate corresponding to the braiding progress, and only after the braiding was complete was the mandrel with the braid still on it immersed in a bath of liquid resin material and then placed in a curing mold. After that, the mandrel was withdrawn. Thus, the Shobert U.S. Pat. No. 3,007,497 discloses only a single braided layer, which is not wet with resin until after the braiding is complete, and does not suggest forming the final tubing on a continuous basis.
Shobert, U.S. Pat. No. 3,033,729, issued May 8, 1962, describes a method of making fiber reinforced tubing on a continuous basis. However, the strands forming the innermost reinforcing fiber layer are not included in a braiding operation but are wetted by resin and fed through apertured guides that distribute the strands evenly about a mandrel. The resin on these strands is partially cured so that the partial structure is sufficiently rigid to allow either a normal braid of the type described in Francis U.S. Pat. No. 2,602,766 or in the Shobert '497 patent to be braided thereon continuously, even at a point beyond the end of the mandrel. The braided strands in the second reinforcing layer are put on dry but are then wetted by the uncured part of the resin on the longitudinal strands forming the first reinforcing layer. The structure is then pulled through a second curing station to be completely cured. Tractive force to move the entire two-layer structure is furnished by way of two endless belts that press firmly against opposite sides of the cured two-layer structure at a location beyond the second curing station.
Shobert U.S. Pat. No. 3,457,962, issued July 29, 1969, describes the fabrication of a hollow fiber reinforced plastic rod having several layers of reinforcing strands. The first layer is a standard braid, as are any further odd-numbered layers, that does not contain stud fill and is not expected to slide on the mandrel. Thus, only rods of limited finite length can be formed. The second layer is formed, as are any further even-numbered layers, of longitudinal fill strands wetted by resin before being applied over the next lower braided strands, and it is the wet resin in the even-numbered layers that wets the braided strands in the odd-numbered layers.
Goldsworthy et al, U.S. Pat. No. 3,769,127 issued Oct. 30, 1973, describes the fabrication of multi-layer fiber reinforced tubing on a continuous basis, but none of the layers is braided and the inner-most layer is longitudinal fill. Other layers are helically wound but lack the interlocking strengthening effect of braided strands. Only the longitudinal fill strands are wetted with liquid matrix material; the helically wound strands derive their wetting from the liquid material on the longitudinal fill strands.